The art is replete with shapes of unused open wire staples for suturing living tissues, and rams and anvils of various shapes used to close such staples. U.S. Pat. Nos. 3,873,016; 4,202,480; 4,256,251; 4,321,002; 4,477,007; 4,477,008; and 4,519,532 provide illustrative examples.
Such prior art unused open wire staples have included a staple having a straight central portion with straight pointed end portions projecting at right angles thereto (such as is illustrated in FIG. 4 of U.S. Pat. No. 4,202,480 incorporated herein by reference), which staple may be bent at two spaced locations along its central portion to form a generally rectangular closed staple (see FIG. 6 of U.S. Pat. No. 4,202,480) and is called a "box" staple herein. The side of the closed box staple opposite its end portions can subsequently be bent into a U-shape to retract the staple from the skin and underlying tissue as is illustrated in U.S. Pat. No. 4,026,520 (incorporated herein by reference). Such box staples have been widely used and have been well accepted by the medical community. This is at least partially so because of the currently preferred method for stapling skin. It is known that the inner surfaces of skin edge portions separated by an injury or an incision must make contact for proper healing to occur, and that if skin edge portions are inverted during stapling (i.e., positioned with their outer surfaces face to face) poor healing with the probability of scarring will result. Thus skin edge portions to be stapled together typically are everted (i.e., tented upwardly) with the inner surface of the skin edge portions pressed together, and the staple is applied over the everted skin edge portions to hold them together. When the box staple is so used, the parts of the skin edge portions pierced by the staple initially are positioned along its aligned end portions on the side of the closed box staple adjacent the skin portions being stapled. With time, tensions in the skin transverse to the opening being stapled closed will cause the parts of the skin portion pierced by the staple to move from around the adjacent end portions (which then become buried in tissue beneath the joined skin portions) to positions around the opposite side portions of the closed staple at which the skin edge portions lose some of their original eversion and are more in alignment. With the box staple, however, this movement of the skin does not occur immediately due to the restriction caused by the right angle corners between the end portions and side portions of the staple around which corners those parts of the skin portions must pass. Thus, the skin portions have a tendency to remain everted along the entire length of the opening being closed at least for the period of time required to complete stapling together of the skin edge portions, and a person who has completed the stapling can visually assure himself after the stapling of the skin edge portions is complete that the skin edge portions are still in a position which will afford proper healing. The box type staple, however, suffers from the disadvantage of requiring the staple to be bent sharply in two locations to close it in a manner which has required the use of metal rams and anvils and the application of substantial closing force; and causes some damage to the skin, particularly when the parts of the skin edge portions pierced by the staple move around the right angle bends in the staple as described above.
Another prior art staple for suturing living tissue described in U.S. Pat. No 4,321,002 comprises a generally U-shaped central portion having at least one arcuate part and curved outer portions terminating in sharp points. That staple can be closed by bending generally straight the arcuate part or parts so that the curved outer portions will smoothly enter and gather living tissue such as skin portions. During such closure the sharp points on the outer portions move to adjacent generally aligned positions to provide a generally D-shaped staple. As with the previously described box staple, the central portion of the closed D-shaped staple can subsequently be bent to retract the outer portions of the staple from the tissue.
The force needed to close such a D-shaped staple having only one arcuate part is substantially reduced for a similarly sized staple from the force required to close the box staple described above, so that the D-shaped staple can be closed with a ram and anvil made of polymeric material such as is described in U.S. Pat. Nos. 4,477,008 and 4,519,532 (incorporated herein by reference). Also the curved outer portions can cause a reduced amount of damage to skin and tissue during use compared to the box staple. Such D-shaped staples, however, have not been received by the medical community with the enthusiasm one might expect presumably in part because the closed D-shaped staple will not hold joined skin portions in an everted position as long as a closed box staple. The stapled skin portions easily and quickly move along the arcuate portions of the D-shaped staple to a generally aligned position (which aligned position provides as good or better healing than the everted position) typically before the person stapling together the skin edge portions has completed the required stapling, so that that person can not observe all of the stapled skin edge portions in an everted position and thus be sure that some of the skin portions will not subsequently become inverted.
Also, even though the closing force of the "D" shaped staple having only one arcuate part is sufficiently low that rams and anvils used to close it can be made of polymeric material, significant wear can occur on such polymeric rams and anvils when they are used to close a large number of staples; and it has been found that staples can slip sideways along the surfaces of the polymeric rams and anvils contacting the staple (a phenomenon not observed between metal anvils, rams and staples) which can result in improperly shaped closed staples.
Another general problem that has existed in the design of rams and anvils for staplers has been to deal with the tendency for the central portion of the open staple to bend away from the anvil toward the ram as a result of forces by which the staple is bent to its closed position. One suggested approach for use with box staples has been to arch the center portion of the open staple toward the anvil so that it bends to a generally straight position as the staple is bent closed as is illustrated in U.S. Pat. No. 4,256,251 (see FIGS. 12 and 19). Another approach being used is to shape the central portion of the ram so that it will straighten the bowed central portion of the staple by bending it against the anvil after the staple is essentially closed as is done in the "Precise".TM. stapler sold for several years by Minnesota Mining and Manufacturing Company, St. Paul, Minn. Yet another approach has been to provide a support to prevent such bending on the side of the central portion of the staple opposite the ram as is described in U.S. Pat. No. 4,127,227.
However prevented, it is preferable that the central portion of the staple is not bowed significantly upwardly after the staple is closed, since if such a bow is present, pressure from the jaws of a staple remover of the type described in U.S. Pat. No. 4,026,520 will cause crank-like forces tending to rotate the staple around its central portion as it is bent open, which rotation of the staple can cause the staple to be bent out of its plane which may damage the tissue from which the staple is being removed.